The present invention relates to gas turbine engines and, more particularly, to aircraft-type high bypass ratio turbine engines having multi-stage compressor and turbine sections.
A typical modern gas turbine aircraft engine, particularly of the high bypass ratio type, includes multi-stage high pressure compressor and turbine sections interconnected by a central compressor shaft or, in some models, a forward shaft. In the latter instance, the forward shaft extends between the webs of the last stage high pressure compressor disk and the first stage high pressure turbine disk. The high pressure turbine section typically includes first and second stage disks in which the second stage disk is attached to the first stage disk by a bolted connection. The interstage volume between the first and second stage turbine disks is enclosed by a seal extending between the outer peripheries of the disks. The seal is generally cylindrical in shape and its wall is outwardly convex in shape.
The first and second stage disks are isolated by a forward face plate, attached to the forward face of the first stage disk, and an aft seal attached to the rearward face of the second stage disk web. Typically, cooling air ducted externally from the compressor section is circulated within the volumes adjacent to the face plate and aft seal, as well as the interstage volume, in order to cool the disks and blades they support. The cooling air is conveyed radially outwardly from the turbine section through channels formed in the turbine blades.
In such engines, virtually all of the connections between components are accomplished through bolting. That is, the forward face plate is connected to the stage one disk by a circular pattern of bolts, extending about the face plate and disk. The inner periphery of the face plate is bolted to a disk positioned forwardly of the first stage disk. Similarly, the interstage thermal seal is connected to the turbine disks through bolts in a circular pattern, typically clamping angular blade retaining rims to the opposite faces of the turbine disks as well. In addition, the second stage disk includes a rearwardly-extending cone which is bolted to the aft seal.
A disadvantage of such bolted connections is that they require holes to be formed in the disks which create stress concentrations and limit the useful lives of the seals and disks. Furthermore, additional disk weight is required to sustain the stresses imposed by the bolt and bolt hole engagements. Accordingly, recent turbine engines have been designed incorporating bayonet connections between the forward faceplate, interstage seal, aft seal and the first and second stage disks. The interstage seal for example includes a forward arm extending towards the first stage disk and an aft arm extending towards the second stage disk. The arms include a reverse catenary contour and include bayonet connection means for attachment with the first and second stage disks.
A disadvantage with such bayonet connections is that alignment of the first and second stage disks and seals is difficult to maintain during operation, which may result in excessive vibrations during operation.
Attempts have been made to prevent axial movement of the interstage seal with respect to the second stage disk by inserting a standard split retaining ring between a slot formed in the interstage seal aft arm and a corresponding slot formed in the second stage disk post. The split ring is an axisymmetric ring which is first inserted in the disk post slot at assembly and then is pushed down to engage the aft seal arm slot for axial retention. During operation of the engine the lower surface of a turbine blade restrains the radial motion of the split ring under centrifugal load. A disadvantage with the use of a split ring is that the slot in the disk post, which extends around the entire circumference of the engine, introduces a life-limiting characteristic to the assembly because of the large stress concentrations present in the slot area. Consequently the disk post is weakened and frequent replacement becomes necessary.
Accordingly, there is a need for mounting the first and second stage disks and interstage seal which minimizes alignment problems and further, there is a need for a design which eliminates axial movement of the interstage seal in connection with the first and second stage disks.